Increasingly, businesses and other entities are using virtualized computing resources (whether running on purchased or leased computer hardware). Virtualized environments are generally very dynamic—virtual machines can easily be spun up, shut down, and moved. A given physical machine may support tens or hundreds of virtual machines and if that machine fails, the images running on the physical machine can be rapidly migrated to one or multiple other physical machines. Unfortunately, virtualized environments can pose problems for firewall rules which tend to rely on static information, such as static IP addresses.